biostudies-literatureUnknown14(12)El-Hassanein AMA novel, simple, affordable, and reliable colorimetric paper-based analytical device (PAD) was developed for the point-of-use quality testing of ethanol-based hand sanitizers, mainly against adulteration by water. The principle was based on the novel solvatochromism of methylparaben (MPB)-Fe³⁺ complex, where water is essential for complex formation and ethanol is necessary for MPB solubility. The intensity of the formed violet color, measured at 528 nm, showed a good correlation (<i>R</i>² = 0.996) with the percentage water in the reaction media over a range from 40% to 100% (0-60% ethanol), with excellent accuracy and precision as indicated by the percent recovery within 100.00% ± 2% and %RSD of <2%. A PAD was prepared by the sequential immobilization of Fe³⁺ ions and MPB on chitosan-modified filter paper. The developed PAD was successfully applied for the quality testing of ethanol-based hand sanitizers using an established color index, where clearly distinct colors were observed as a function of the percentage ethanol (0-100%). The developed test strips could achieve on-site lab-quality results without expensive or sophisticated instruments using a few milligrams of FeCl₃ and MPB in addition to regular filter paper. Accordingly, it can be used as a test strip for the quality checking of ethanol-based hand sanitizers by end users.RSC advances8188-8194https://www.ebi.ac.uk/biostudies/studies/S-EPMC10925907biostudies-literatureSimple colorimetric paper-based test strip for point-of-use quality testing of ethanol-based hand sanitizers.PMC10925907El-Hassanein AMMansour FRHammad SFAbdella AAfalseSimple colorimetric paper-based test strip for point-of-use quality testing of ethanol-based hand sanitizers.A novel, simple, affordable, and reliable colorimetric paper-based analytical device (PAD) was developed for the point-of-use quality testing of ethanol-based hand sanitizers, mainly against adulteration by water. The principle was based on the novel solvatochromism of methylparaben (MPB)-Fe³⁺ complex, where water is essential for complex formation and ethanol is necessary for MPB solubility. The intensity of the formed violet color, measured at 528 nm, showed a good correlation (<i>R</i>² = 0.996) with the percentage water in the reaction media over a range from 40% to 100% (0-60% ethanol), with excellent accuracy and precision as indicated by the percent recovery within 100.00% ± 2% and %RSD of <2%. A PAD was prepared by the sequential immobilization of Fe³⁺ ions and MPB on chitosan-modified filter paper. The developed PAD was successfully applied for the quality testing of ethanol-based hand sanitizers using an established color index, where clearly distinct colors were observed as a function of the percentage ethanol (0-100%). The developed test strips could achieve on-site lab-quality results without expensive or sophisticated instruments using a few milligrams of FeCl₃ and MPB in addition to regular filter paper. Accordingly, it can be used as a test strip for the quality checking of ethanol-based hand sanitizers by end users.2024-01-01T00:00:00Z2024 Mar2025-04-04T21:31:06.068Z2025-04-04T21:31:06.068ZS-EPMC109259073846919810.1039/d3ra08110a